Accuracy of 18F-Fluorodeoxyglucose Positron Emission Tomography in Early Metastatic Testicular Seminoma: Analysis From the SEMS Trial

Abstract

Purpose: Recent clinical trials on primary retroperitoneal lymph node dissection (RPLND) for testicular seminoma highlight inaccuracies in conventional imaging for lymph node staging. Limited data exist on the accuracy of positron emission tomography (PET) in patients with chemotherapy-naïve testicular seminoma. We evaluated the accuracy of 18F-fluorodeoxyglucose (FDG) PET for the detection of metastatic disease within the SEMS (Surgery in Early Metastatic Seminoma) trial.

Materials and methods: The SEMS trial is a phase 2 prospective study evaluating efficacy of primary RPLND in patients with testicular seminoma with limited retroperitoneal lymphadenopathy. 18F-FDG PET scanning was performed as a radiographic correlate in addition to standard axial imaging before surgery. PET findings were based on local interpretation, and the results were compared with surgical pathology.

Results: Of the 55 patients enrolled in the trial, 26 (47%) underwent PET. Twenty (77%) scans were reported as positive with lymph nodes in the retroperitoneum, pelvis, or inguinal region. Of the positive PET scans, 18 had pathologically positive lymph nodes (positive predictive value 90%) at the time of RPLND. Six PET scans were negative with 5 of these patients having surgically confirmed pN0 disease (negative predictive value 83%). Sensitivity of PET for detecting lymph node metastatic seminoma was 95% and specificity was 71%. The average standardized uptake values of the PET-positive lymph nodes and pathologically positive lymph nodes were 7.0 (range 2.6-18.8) and 6.8 (range 1.53-18.8), respectively. No PET-positive lesions outside of the retroperitoneum or pelvis were found to represent metastatic seminoma on clinical follow-up.

Conclusions: In patients with testicular seminoma, 18F-FDG PET findings correlated with both pathologically positive and negative retroperitoneal lymph nodes in most cases. Further research is needed to determine if PET can improve on the already good predictive performance of conventional imaging and clinical expertise.

Keywords: diagnosis; neoplasm staging; positron-emission tomography; predictive value of tests; seminoma.